1. Field of the Invention
The present invention relates to improvements in solid-state fluid circuit systems for effecting controlled transport of liquids and/or gas substances. More particularly, it relates to improved valve structures for selectively providing fluid communication between spaced fluid passageways within such circuit systems.
2. Background Art
In applications where it is necessary to transport and process small quantities of liquid or gas substances in a highly controlled and precise manner, such as in biological liquid analyzers or gas chromatography systems, solid-state fluid circuit systems are gaining in popularity. Such solid-state fluid circuit systems typically comprise a solid plastic plate, usually comprising a laminated structure of two or more plastic plates, having a network of internal passageways for conducting pressurized fluid from one location to another. Various fluid-control devices, i.e. valves, and fluid sensors are located along such passageways to control the movement of the fluid between the passageways and to process the fluid as required. A key component to the effectiveness of any such fluid circuit system is the valving mechanism used to selectively provide a fluid communication between the spaced passageways.
A common approach for constructing valving mechanisms for fluid circuit systems of the above type has been to position a continuous membrane sheet atop a rigid substrate having a planar surface which has been milled-out, chemically etched or otherwise grooved, to define spaced fluid passageways, and to provide means for selectively moving portions of that membrane towards and away from a land portion separating the opposing passageways to respectively prevent and enable fluid communication between the passageways. U.S. Pat. No. 4,304,257 discloses such a valving structure wherein solenoid-operated actuators are affixed to selected portions of such a membrane sheet to mechanically move their respective attached sheet portions towards and away from the land separating spaced passageways. U.S. Pat. No. 5,203,368 discloses a similar valve structure wherein the membrane is pneumatically moved by suction or pressure applied to the side of a continuous sheet membrane that is opposite the fluid flow passageways. U.S. Pat. Nos. 5,083,742 and 5,176,359 disclose a valve mechanism similar to the aforementioned mechanisms, but wherein the membrane sheet is constructed to have a plurality of blister portions that form domes over the lands between spaced fluid passageways. These blister portions have self-restoring forces that normally urge them into their domed condition. Pneumatic actuators are provided for introducing a pressurized fluid into a chamber above each dome in order to flatten the dome into contact with the land between the spaced passageways and thereby disrupt fluid communication between the spaced fluid passageways.
While all of the above-noted valving structures are useful for controlling fluid flow in solid-state fluid circuits of the type described, all suffer significant problems with respect to fluid leakage. This is mainly due to the difficulty in bonding the dissimilar materials that constitute the flexible membrane and the sandwiching or underlying rigid substrates. Such leakage can allow escape of the transported fluid and/or unintended movement of valve elements, due to decreased "holding" pressure on the membrane portions at the open/close region.
U.S. Pat. No. 5,496,009 discloses an approach for avoiding the above-noted leakage problems. Rather than using a single flexible membrane that encompasses the entire surface area of a pair of confronting plates that cooperate to define a network of fluid passageways along which multiple valves are positioned, this approach uses a plurality of discrete flexible diaphragm disks. Each diaphragm disk is positioned within one of a plurality of small valve chambers formed in one of the plates, each valve chamber containing a pair of spaced fluid ports which, by virtue of the valve structure, are to be selectively fluidically connected. The peripheral edge of each disk is sandwiched between the confronting plates to hold the disk in a position overlying the ports. A control port is provided through one plate to access that side of the diaphragm that is opposite the fluid ports, and the diaphragm is moved towards and away from the fluid ports, to respectively close and open fluid communication therebetween, by application of positive or negative pressure to the control port. Since the surface area of each disk is only slightly larger than the respective surface area of the valve chambers, the disks themselves do not significantly interfere with the lamination process of bonding the plates together; thus, the aforementioned leaking of fluid is minimized. While this device is improved significantly with respect to inter-substrate leakage, it is disadvantageous in that it relies upon a pneumatic pressure differential to control movement of a flexible diaphragm member; this presents a problem in maintaining the valve closed over an extended period against positive pressure fluids in the transport passage. Affixing a mechanical actuator to such a thin compliant member would present bonding/attachment difficulties and would be contrary to the patentee's design approach, which is to provide a flexibly conforming seal construction at the diaphragm/flow passage interface. Further, there is still an opportunity for fluid to leak past the edges of the diaphragm disk and into the control port used to deflect the diaphragm disk.